This invention relates to a catalyst composition useful for converting a hydrocarbon to a C6 to C8 aromatic hydrocarbon, to a process for producing the composition, and to a process for using the composition for converting a hydrocarbon to a C6 to C8 aromatic hydrocarbon.
It is well known to those skilled in the art that aromatic hydrocarbons are a class of very important industrial chemicals which find a variety of uses in petrochemical industry. It is also well known to those skilled in the art that catalytically cracking gasoline-range hydrocarbons produces aromatic hydrocarbons such as, for example, benzene, toluene, and xylenes (hereinafter collectively referred to as BTX) in the presence of catalysts which contain a zeolite. The product of this catalytic cracking process contains a multitude of hydrocarbons including unconverted C5+ alkanes, C5+ alkenes, C5+ cycloalkanes, or combinations of two or more thereof; lower alkanes such as methane, ethane, and propane; lower alkenes such as ethylene and propylene; and C9+ aromatic hydrocarbons. Recent efforts to convert gasoline to more valuable petrochemical products have therefore focused on improving the conversion of gasoline to more valuable aromatic hydrocarbons in the presence of zeolite catalysts. For example, a gallium-promoted zeolite ZSM-5 has been used in the so-called Cyclar Process to convert a hydrocarbon to BTX. The aromatic hydrocarbons can be useful feedstocks for producing various organic compounds and polymers. However, heavier, less useful aromatic compounds having 9 or more carbon atoms per molecule are also produced by the conversion process. Furthermore, a zeolite catalyst is generally deactivated in a rather short period because of depositions of carbonaceous material, generally coke, on the surface of the catalyst. Therefore, development of a catalyst and a process for converting non-aromatic hydrocarbons to the more valuable BTX in which the process and catalyst reduce the depositions of the carbonaceous material would be a significant contribution to the art and to the economy.
An object of this invention is to provide a catalyst composition which can be used to convert a hydrocarbon to a C6 to C8 aromatic hydrocarbon. Also an object of this invention is to provide a process for producing the catalyst composition. Another object of this invention is to provide a process which can employ the catalyst composition to convert a hydrocarbon to a C6 to C8 aromatic hydrocarbon. An advantage of the catalyst composition is that it enhances the production of BTX. Other objects and advantages will becomes more apparent as this invention is more fully disclosed hereinbelow.
According to a first embodiment of the present invention, a composition which can be used as a catalyst for converting a hydrocarbon or a hydrocarbon mixture to a C6 to C8 aromatic hydrocarbon is provided. The composition is an aluminosilicate which comprises, a silica, an alumina, and a metal selected from the group consisting of nickel, palladium, molybdenum, gallium, platinum and combinations of any two or more thereof wherein the weight ratio of elemental aluminum to elemental silicon is in the range of from about 0.002:1 to about 0.6:1 and the weight ratio of the metal to silicon is in the range of from about 0.0005:1 to about 0.1:1.
According to a second embodiment of the present invention, a process which can be used for producing a catalyst composition is provided. The process comprises the steps: (1) contacting a zeolite, which comprises or consists essentially of silicon and aluminum, with an acid in an amount and under a condition effective to reduce the aluminum content of the zeolite to produce an aluminum-reduced zeolite; (2) contacting said aluminum-reduced zeolite with a metal compound whose metal is selected from the group consisting of nickel, palladium, molybdenum, gallium, platinum, and combinations of any two or more thereof under a condition effective to impregnate the metal compound or the metal onto the aluminum-reduced zeolite to produce a metal-impregnated, alumina-reduced zeolite; and optionally (3) treating the metal-impregnated aluminum-reduced zeolite with a reducing agent under a condition effective to lower the oxidation state of the metal in the metal-impregnated, aluminum-reduced zeolite.
According to a third embodiment of the present invention, a process which can be used for converting a hydrocarbon or a hydrocarbon mixture to a C6 to C8 aromatic hydrocarbon for reducing the deposition of carbonaceous material on the surface of a catalyst is provided which comprises, consists essentially of, or consists of, contacting a fluid which comprises a hydrocarbon or a hydrocarbon mixture with a catalyst composition which is the same as disclosed above in the first embodiment of the invention under a condition effective to convert a hydrocarbon to an aromatic hydrocarbon containing 6 to 8 carbon atoms per molecule.
The catalyst composition of the first embodiment of the present invention is an aluminosilicate which can comprise, consist essentially of, or consist of a coke-reducing amount of a metal selected from the group consisting of nickel, palladium, molybdenum, gallium, platinum, and combinations of any two or more thereof.
According to the present invention, the term xe2x80x9ccokexe2x80x9d refers to a semi-pure carbon generally deposited on the surface of a metal wall or a catalyst. The weight ratio of aluminum to silicon can be any ratio that is effective to convert an aliphatic hydrocarbon to an aromatic hydrocarbon. Generally, the weight ratio of element aluminum to element silicon can be in the range of from about 0.002:1 to about 0.6:1, preferably about 0.005:1 to about 0.5:1, and most preferably 0.006:1 to 0.4:1. The weight ratio of the metal to element silicon can be in the range of from about 0.0001:1 to about 0.1:1, preferably about 0.0005:1 to about 0.05:1, more preferably about 0.001:1 to about 0.04:1, and most preferably 0.002:1 to 0.03:1.
Alternatively, the weight of element aluminum in the invention composition can be in the range of from about 0.1 to about 10, preferably about 0.2 to about 8, and most preferably 0.5 to 5 grams per 100 grams of the composition. The weight of element silicon in the invention composition can be in the range of from about 20 to about 50, preferably about 25 to about 45, and most preferably 30 to 40 grams per 100 grams of the composition. The weight of the metal can be in the range of from about 0.001 to about 10, preferably about 0.01 to about 5, and most preferably 0.1 to 2 grams per 100 grams of the composition. The composition can also be characterized by having the following physical characteristics: a micropore surface area, as determined by the BET method using nitrogen, in the range of from about 250 to about 600, preferably 300 to 500 m2/g; a micropore pore volume in the range of from about 0.01 to about 0.8, preferably about 0.01 to about 0.75 ml/g; an average micropore pore diameter in the range of from about 10 to about 300, preferably about 10 to about 250 xc3x85; and a porosity of more than about 30%. Detailed physical property analyses are disclosed hereinbelow in the Examples section.
The aluminosilicate or zeolite component of the composition of the present invention can be prepared by combining any alumina and any silica in the element weight ratios disclosed above under any conditions sufficient to effect the formation of a zeolite according to any methods well known to one skilled in the art. However, it is presently preferred that the composition of the present invention be produced by the process disclosed in the second embodiment of the invention. In the first step of the second embodiment of the invention, a zeolite is contacted with an acid under a condition sufficient to effect the formation of an aluminum-reduced zeolite.
Any commercially available zeolites can be employed as a starting material of the process of the second embodiment of the invention. Examples of suitable zeolites include, but are not limited to, those disclosed in Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 15 (John Wiley and Sons, New York, 1991) and in W. M. Meier and D. H. Olson, xe2x80x9cAtlas of Zeolite Structure Types,xe2x80x9d pages 138-139 (Butterworth-Heineman, Boston, Mass., 3rd ed. 1992). ZSM-5 and similar zeolites that have been identified as having a crystalline framework topology or structure identified as MFI are particularly preferred because of their shape selectivity. A zeolite can further comprise or be combined with an inorganic binder such as alumina, silica, alumina-silica, aluminum phosphate, clay (such as, for example, bentonite), and combinations of any two or more thereof.
Generally, any organic acids, inorganic acids, or combinations of any two or more thereof can be used in the process of the present invention so long as the acid can reduce the aluminum content in the zeolite. The acid can also be a diluted aqueous acid solution. Examples of suitable acids include, but are not limited to sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, ammonium sulfate, ammonium chloride, ammonium nitrate, formic acid, acetic acid, trifluoroacetic acid, citric acid, trichloroacetic acid, p-toluenesulfonic acid, methanesulfonic acid, partially neutralized acids, wherein one or more protons have been replaced with, for example, a metal (preferably an alkali metal), and combinations of any two or more thereof. Examples of partially neutralized acids include, but are not limited to, sodium bisulfate, sodium dihydrogen phosphate, potassium hydrogen tartarate, and combinations thereof. The presently preferred acids are hydrochloric acid and nitric acid for they are readily available.
Any methods known to one skilled in the art for treating a solid catalyst with an acid can be used in the acid treatment of the present invention. Generally, a zeolite material can be suspended in an acid solution. The concentration of the zeolite in the acid solution can be in the range of from about 0.01 to about 500, preferably about 0.1 to about 400, more preferably about 1 to about 350, and most preferably 5 to 300 grams per liter. The amount of acid required is the amount that can maintain the solution in acidic pH during the treatment. Preferably the initial pH of the acid solution containing a zeolite is adjusted to lower than about 6, preferably lower than about 4, more preferably lower than about 3, and most preferably lower than 2. Upon the pH adjustment of the solution, the solution can be subjected to a treatment at a temperature in the range of from about 30xc2x0 C. to about 200xc2x0 C., preferably about 50xc2x0 C. to about 150xc2x0 C., and most preferably 70xc2x0 C. to 120xc2x0 C. for about 10 minutes to about 30 hours, preferably about 30 minutes to about 25 hours, and most preferably 1 to 20 hours. The treatment can be carried out under a pressure in the range of from about 1 to about 10 atmospheres (atm), preferably about 1 atm. Thereafter, the acid-treated zeolite material can be washed with a running water for 1 to about 60 minutes followed by drying, at about 50 to about 200, preferably about 75 to about 175, and most preferably 100 to 150xc2x0 C. for about 0.5 to about 15, preferably about 1 to about 12, and most preferably 1 to 10 hours, to produce an aluminum-reduced or acid-leached zeolite. Any drying method known to one skilled in the art such as, for example, air drying, heat drying, spray drying, fluidized bed drying, or combinations of two or more thereof can be used.
The dried, aluminum-reduced zeolite can also be further washed, if desired, with a mild acid solution such as, for example, ammonium nitrate which is capable of maintaining the pH of the wash in acidic range. The volume of the acid generally can be the same volume as the acid for reducing the alumina content in a zeolite. The mild acid treatment can be carried out under substantially the same conditions disclosed in the acid treatment for reducing alumina content in a zeolite. Thereafter, the resulting solid can be washed and dried as disclosed above.
The dried, aluminum-reduced zeolite, whether it has been further washed with a mild acid or not, can be calcined under a condition known to those skilled in the art. Generally such a condition can include a temperature in the range of from about 250 to about 1,000, preferably about 350 to about 750, and most preferably 450 to 650xc2x0 C. and a pressure in the range of from about 0.5 to about 50, preferably about 0.5 to about 30, and most preferably 0.5 to 10 atmospheres (atm) for about 1 to about 30 hours, preferably about 2 to about 20 hours, and most preferably 3 to 15 hours.
Thereafter, the aluminum-reduced zeolite, whether it has been calcined or not, is impregnated thereon with a metal compound whose a metal selected from the group consisting of nickel, palladium, molybdenum, gallium, platinum, and combinations of any two or more thereof. Any metal compound that can promote the impregnating of the aluminum-reduced zeolite with the metal of the metal compound can be employed in the present invention. Examples of such metal compounds include, but are not limited to, nickel chloride, nickel bromide, nickel nitrate, nickel sulfate, nickel hydroxide, palladium chloride, palladium nitrate, palladium sulfate, palladium acetate, palladium hydroxide, molybdenum chloride, molybdenum bromide, chloroplatinic acid (H2PtCl6.xH2O), platinum (IV) chloride (platinic chloride), platinum (II) bromide, platinum (II) iodine, tetramine platinum (II) chloride (Pt(NH3)4Cl2.H2O or Pt(NH3)4Cl2), tetramine platinum (II) nitrate (Pt(NH3)4(NO3)2), tetramine platinum (II) hydroxide (Pt(NH3)4(OH)2), tetrachlorodiamine platinum (IV), gallium acetate (basic), gallium trifluoride, gallium trichloride, gallium, gallium hydroxide, gallium nitrate, gallium sulfate, and combinations of any two or more thereof. The presently preferred metal compounds are chloroplatinic acid and gallium nitrate for they are readily available.
A metal-promoted or metal-impregnated, aluminum-reduced zeolite can be prepared by any suitable, effective means so long as the resulting zeolite can be used in the process of the present invention. Preferably, the aluminum-reduced or acid-leached zeolite, which can have been compounded with a binder as described above and have been shaped by any means known in the art such as, for example, pelletized, extruded, tableted, or combinations of two or more thereof, can be impregnated such as, for example, by incipient wetness method with a solution, preferably aqueous solution, containing a suitable metal compound disclosed above. The concentrations of the metal compound in the impregnating solution and the weight ratio of this solution to the zeolite are chosen such as to provide a finished, metal-impregnated, aluminum-reduced zeolite which contains the desired content of metal which can effect the reduction of coke deposition on the surface of the composition of the present invention as disclosed above in the first embodiment of the present invention.
After the impregnation with a metal compound has been completed, the metal-impregnated, aluminum-reduced zeolite can then be dried, as disclosed above and then calcined. Generally the calcination is carried out in air under the pressure range disclosed above for calcining the aluminum-reduced zeolite. The calcination can also be carried out at a temperature in the range of about 300 to about 1000xc2x0 C. for about 1 to about 30 hours, preferably about 400xc2x0 C. to about 800xc2x0 C. for 2 to about 20 hours, and most preferably 450xc2x0 C. to 650xc2x0 C. for 3 to 15 hours.
The calcined metal-impregnated, aluminum-reduced zeolite can then be treated with a reducing agent to reduce the oxidation state of the metal. For example, if the metal is platinum, the oxidation state of platinum is reduced to 0 whereas gallium""s oxidation state can be reduced to 1. The presently preferred reducing agent is a hydrogen-containing fluid which comprises molecular hydrogen (H2) in the range of from 1 to about 100, preferably about 5 to about 100, and most preferably 10 to 100 volume %. The reduction can be carried out at a temperature, in the range of from about 250xc2x0 C. to about 800xc2x0 C. for about 0.1 to about 10 hours preferably about 300xc2x0 C. to about 700xc2x0 C. for about 0.5 to about 7 hours, and most preferably 350xc2x0 C. to 550xc2x0 C. for 1 to 5 hours. If the calcined metal-impregnated, aluminum-reduced zeolite is not first treated with a reducing agent, the composition of the present invention can be treated with a reducing agent as described herein prior to use of the composition of the invention.
Upon completion of the above-described treatment or impregnation of an aluminum-reduced or acid-leached zeolite with a metal compound, a metal-promoted zeolite composition is produced which can then be used in the third embodiment of the present invention.
According to the third embodiment of the present invention, a process useful for converting an aliphatic hydrocarbon or a hydrocarbon mixture to a mixture rich in C6 to C8 aromatic hydrocarbons comprises, consists essentially of, or consists of contacting a fluid stream with a catalyst composition, optionally in the presence of a hydrogen-containing fluid, under a condition sufficient to enhance or effect the conversion of a hydrocarbon to a mixture rich in C6 to C8 aromatic hydrocarbons wherein said fluid stream comprises a hydrocarbon or hydrocarbon mixture which comprises paraffins, olefins, naphthenes. Aromatic compounds can also be present in the fluid in some minor amounts. The catalyst composition is the same as that disclosed in the first embodiment of the invention which can be prepared by the second embodiment of the invention.
The term xe2x80x9cfluidxe2x80x9d is used herein to denote gas, liquid, vapor, or combinations thereof. The term xe2x80x9chydrocarbonxe2x80x9d is generally referred to, unless otherwise indicated, as one or more hydrocarbons having from about 4 carbon atoms to about 25 carbon atoms, preferably about 5 to about 20 carbon atoms, and most preferably 5 to 16 carbon atoms per molecule. The term xe2x80x9cenhancexe2x80x9d refers to an increased BTX in the product employing the catalyst composition as compared to employing a non-acid-leached zeolite. Examples of a hydrocarbon include, but are not limited to, butane, isobutanes, pentane, isopentanes, hexane, isohexanes, cyclohexane, methylcyclohexane, heptane, isoheptanes, octane, isooctanes, nonanes, decanes, undecanes, dodecanes, tridecanes, tetradecanes, pentadecanes, hexadecanes, butenes, isobutene, pentenes, hexenes, and combinations of any two or more thereof. In some feed fluids, such as, for example, gasoline can comprise some benzene, toluene, ethylbenzene, and xylenes.
Any fluid which contains a hydrocarbon as disclosed above can be used as the feed for the process of this invention. Generally, the fluid feed stream can also contain olefins, naphthenes (cycloalkanes), or some aromatic compounds. Examples of suitable, available fluid feeds include, but are not limited to, gasolines from catalytic oil cracking processes, pyrolysis gasolines from thermal cracking of saturated hydrocarbons, naphthas, gas oils, reformates, and combinations of any two or more thereof. The origin of this fluid feed is not critical. Though particular composition of a feed is not critical, a preferred fluid feed is derived from gasolines which generally contain more paraffins (alkanes) than combined content of olefins, cycloalkanes, and aromatic compounds.
Any hydrogen-containing fluid which comprises, consists essentially of, or consists of, molecular hydrogen (H2) can be used in the process of this invention. This hydrogen-containing fluid can therefore contain H2 in the range of from about 1 to about 100, preferably about 5 to about 100, and most preferably 10 to 100 volume %. If the H2 content in the fluid is less than 100%, the remainder of the fluid may be any inert gas such as, for example, N2, He, Ne, Ar, steam, or combinations of any two or more thereof, or any other fluid which does not significantly affect the process or the catalyst composition used therein.
The contacting of a fluid feed stream containing a hydrocarbon with a hydrogen-containing fluid in the presence of the catalyst composition can be carried out in any technically suitable manner, in a batch or semicontinuous or continuous process, under a condition effective to convert a hydrocarbon to a C6 to C8 aromatic hydrocarbon. Generally, a fluid stream as disclosed above, preferably being in the vaporized state, is introduced into an aromatization reactor having a fixed catalyst bed, or a moving catalyst bed, or a fluidized catalyst bed, or combinations of any two or more thereof by any means known to one skilled in the art such as, for example, pressure, meter pump, and other similar means. Because an aromatization reactor and aromatization process are well known to one skilled in the art, the description of which is omitted herein for the interest of brevity. The condition of the process of the invention can include a weight hourly space velocity (WHSV) of the fluid feed stream in the range of about 0.01 to about 100, preferably about 0.05 to about 50, and most preferably 0.1 to 30 g feed/g catalyst/hour. The hydrogen-containing fluid (gas) hourly space velocity generally is in the range of about 1 to about 10,000, preferably about 5 to about 7,000, and most preferably 10 to 5,000 ft3 H2/ft3 catalyst/hour. Generally, the pressure can be in the range of from about 0 to about 1000 psig, preferably about 0 to about 200 psig, and most preferably 0 to 100 psig, and the temperature is about 250 to about 1000xc2x0 C., preferably about 300 to about 750xc2x0 C., and most preferably 400 to 650xc2x0 C.
The process effluent generally contains a light gas fraction comprising hydrogen and methane; a C2-C3 fraction containing ethylene, propylene, ethane, and propane; an intermediate fraction including non-aromatic compounds higher than 3 carbon atoms; a BTX aromatic hydrocarbons fraction (benzene, toluene, ortho-xylene, meta-xylene and para-xylene); and a C9+ fraction which contains aromatic compounds having 9 or more carbon atoms per molecule. Generally, the effluent can be separated into these principal fractions by any known methods such as, for example, fractionation distillation. Because the separation methods are well known to one skilled in the art, the description of which is omitted herein. The intermediate fraction can be recycled to an aromatization reactor described above; methane, ethane, and propane can be used as fuel gas or as a feed for other reactions such as, for example, in a thermal cracking process to produce ethylene and propylene. The olefins can be recovered and further separated into individual olefins by any method known to one skilled in the art. The individual olefins can then be recovered and marketed. The BTX fraction can be further separated into individual C6 to C8 aromatic hydrocarbon fractions. Alternatively, the BTX fraction can undergo one or more reactions either before or after separation to individual C6 to C8 hydrocarbons so as to increase the content of the most desired BTX aromatic hydrocarbon. Suitable examples of such subsequent C6 to C8 aromatic hydrocarbon conversions are disproportionation of toluene (to form benzene and xylenes) involving transalkylation benzene and xylenes (to form toluene), and isomerization of meta-xylene and/or ortho-xylene to para-xylene.
After the catalyst composition has been deactivated by, for example, coke deposition or feed poisons, to an extent that the feed conversion and/or the selectivity to the desired ratios of olefins to BTX have become unsatisfactory, the catalyst composition can be reactivated by any means known to one skilled in the art such as, for example, calcining in air to bum off deposited coke and other carbonaceous materials, such as oligomers or polymers, preferably at a temperature of about 400 to about 1000xc2x0 C. The optimal time periods of the calcining depend generally on the types and amounts of deactivating deposits on the catalyst composition and on the calcination temperatures. These optimal time periods can easily be determined by those possessing ordinary skills in the art and are omitted herein for the interest of brevity.